1. Technical Field
The disclosure relates to a focused ion beam apparatus provided with a gas electric field ionization ion source (GFIS) and a control method thereof.
2. Description of Related Art
In the related art, as a device that observes an image at high resolution, a scanning electron microscope (SEM) using an electron beam is widely known. Further, in recent years, a scanning electron microscope using helium ions emitted from a gas electric field ionization ion source (GFIS) has also been in practical use.
As a device that machines a random position, a machining device using gallium ions emitted from a liquid metal ion source (LIMS) is widely known. This device is used for cross-section observation of an arbitrary location of a sample, manufacturing of a TEM sample, wiring change of a semiconductor, pattern modification of a semiconductor lithography mask or the like. Further, in recent years, a machining device using an electron beam has been in practical use for the modification of the mask mentioned above.
As a device that machines an arbitrary position of a sample, a micromachining technique using gallium ions is widely used as a general technique, but a micromachining technique using electrons or helium ions is yet considered as a special technique. As the micromachining technique using electrons or helium ions, for example, techniques disclosed in JP-A-2003-328261 and JP-T-2009-517840 are in practical use.
In the machining technique using the gallium ion beam, any materials can be etched by a sputtering effect, but damage to a sample from gallium injection is serious.
On the other hand, in the case of the machining technique using the electron beam or the helium ion beam, damage to a sample is slight, but since it is necessary to use a gas having an etching promotion function, it is difficult to perform machining in a case where an appropriate gas is not present.
In the case of the GFIS machining technique that has been in practical use in recent years, it is possible to exchange ion species by the same device. Thus, in a case where the mass of the ion species is large, it is possible to achieve a machining characteristic close to the machining technique using the gallium ion beam; whereas in a case where the mass of the ion species is small, it is possible to achieve a machining characteristic close to the machining technique using the electron beam. Which ion mass is used is determined based on a desired machining characteristic.
When a machining device is actually used, there is a case where it is necessary to use both of ions having a large mass and ions having a small mass. First of all, there is a case where several kinds of samples are present and ion species suitable for the samples are different from each other. Further, there is a case where one ion species is suitable for machining while the other ion species is suitable for observation, that is, a case where machining performance and image resolving power are not compatible using a single ion species.
In such a case, the ion species is exchanged to cope therewith.
As a method of exchanging the ion species, in addition to exchanging of a source gas to be supplied to the ion source chamber, the following methods may be considered, a method of exchanging an emitted ion species by supplying plural source gases into an ion source chamber at the same time and exchanging an extraction voltage, or a method of extracting only a desired ion species using an E×B (secondary electron detector) from ion species emitted at the same time.
In the former method (i.e., exchanging an emitted ion species), in a case where electric field intensities that ionize gases to be used are close to each other, there is provided a beam in which plural ion species are constantly mixed. Thus, when it is necessary to perform machining using ion species having a small mass, ion species having a large mass may be mixed, and in this case, damage to a sample becomes serious.
In the latter method (i.e., extracting only a desired ion species), a beam of a single ion species is obtained, but an ion optical system is complicated and enlarged, and a beam diameter may not be narrowed down.
That is, according to the both above-mentioned methods, since it is difficult to prevent performance deterioration, the method of exchanging the source gas to be supplied to the ion source chamber is considered again. However, in this case, if the gas before exchange remains in the ion source chamber, the gas is mixed into a beam after exchange. Thus, in this method, it is necessary to wait until the purity of the gas after exchange increases, which causes a problem that an ion species exchange time becomes long.